Private network-to-network interfaces (PNNI) refers to very large ATM networks that communicate between multiple private networks. Depending on the number of nodes served by the PNNI network, the architecture may be flat (non-hierarchical) or may have two or more hierarchical levels. When the network topology moves to multiple level architecture, several new effects on network performance are introduced. A primary motive for introducing new levels in a PNNI network is to increase routing efficiency and reduce call set-up time. However, added levels increase cost and management complexity. Thus there is an important trade-off when considering adding new hierarchical levels.
A typical PNNI network is organized in peer groups. These are subunits of the total network that are interconnected as a group, with each group then interconnected in the PNNI network. An advantage of this architecture is that communications between members in a peer group can be independent of overall network management. When a communication between a node in one peer group and a node in another peer group is initiated, the PNNI protocol is used for that call set-up and management. The size of the peer groups, i.e. the number of nodes in each peer group, also affects the overall performance of the PNNI network. Methods for optimizing peer group size are described and claimed in my co-pending application Ser. No. 10/918,913, filed Aug. 16, 2004.
To make an accurate evaluation of the trade-off described above requires that the changes in call set-up times when a new hierarchical level is added be known with a high confidence level.